1. Field of the Invention
This invention relates to directional control systems, and particularly to an attitude control system for a space vehicle.
2. General Description of the Prior Art
As space vehicles have been made larger, the problems associated with controlling their flight characteristics have vastly increased. In order to provide the needed sophistication in control systems, delicate and bulky apparatuses are required, and this often necessitates locating the control sensors spaced substantially from the engines, typically locating the control sensors in the nose region of the vehicle. Since a space vehicle is not a rigid object, vibrations and resonances develop, wherein movement of one portion of the vehicle is typically not in phase with movement of another portion of the vehicle. As a result, the attitude of the vehicle at one location is often not the same as the attitude elsewhere on the vehicle. The magnitude of this difference becomes particularly large when the attitude of the vehicle at the nose of the vehicle is instantaneously compared with the attitude of the vehicle at the tail of the vehicle. The difference reflects bending moments which exist along the length of the vehicle and complex compensations must typically be applied to control signals derived from attitude measurements in the nose of the vehicle to produce optimum commands to gimbaled engines located at the tail of the vehicle. The compensations are determined from extensive ground vibration tests of the vehicle and from elaborate computations which take into account propellant depletions and payloads for a particular flight. Not infrequently, however, after initial tests and computations are made, new flight plans are developed, necessitating new tests and computations. The result is a tremendously expensive effort in determining answers to stabilization questions.